Thursday, January 01, 2009

Cleaning House on Leopard Server

If you administer OS X servers, chances are the holidays are a time when projects to perform IMACs (1) are often done. Projects that involve moving drives or data. On Leopard Server, to get a clean start for 2009, there are a few command line techniques to note regarding permissions for files and folders. Note, setting permissions in Finder on OS X Server is notoriously buggy, so 9 out of 10 administrators (in white coats, of course) recommend using the command line. Try it: your friends will envy you and the girls will admire you. But first, a word about how permissions work in Leopard Server.

(1). Install, Move, Add or Change.

The Concept of "Effective Permissions"

A user's "Effective Permissions" are the combination of their POSIX access plus their combination or union of relevant ACL allow entries, less their union of relevant ACL deny entries. That's the original Unix base permissions combined with the effect of the Apple Access Control Lists.

Effective Permissions = POSIX + ACL Allow - ACL Deny

It should be noted therefore that ACL Deny entries have the most power and override ACL Allow entries or POSIX permissions.

What happens when a new file or folder is created in a Leopard sharepoint? Here's how it ends up:

POSIX owner - the user who creates the item.

POSIX group - the POSIX group of the enclosing / parent folder.

POSIX permissions - set by umask (where 0755 is the default).

ACL - If any ACL entries on the parent folder have either or both of the file_inherit or directory_inherit controls, then the newly-created item will inherit those ACL entries.

If you are setting permissions on already-created objects, it's critical to note that Finder permissions operations are buggy. I have had decent success with Server Administrator's "Sharing" section (per server, not service) permission settings for sharepoints, and with CLI commands. Either way, you must be sure to propagate any changes: if in Server Administrator, that selection's in the little gear icon, and if from the CLI, that's usually done with a "-R" on the command, for "recursive". The caveat is, for child objects, permissions will propagate only when the child item is not in use (i.e. is not locked).

A New Year's Cleanup Scenario

Let's say a client has asked you to take a drive of old data and share it. This data was collected up from various places, and has been connected to various systems. Your task is to hook the drive up to a Leopard Server, and share it via SMB or AFP. Several commands come in handy here. Let's take a look.

See what you've got. If you take a look at a drive that has been swapped around from machine to machine, it might have a fair amount of detritus, being a mix of permissions, ACLs and owners. A simple ls command can show you what you have in terms of POSIX permissions and ACLs, with these commands respectively.

ls -la

ls -el

The ls -el command is similar to -la, but just shows the ACL if it exists. This is what it might look like, with a typical POSIX perms line showing the group and owner as "_unknown", as well as a couple ACL entries:

Recursively unlock. Because you need unlocked files to perform permission settings, you can start by recursively unlocking a folder, like this. Use sudo if you are not logged or su'ed in as root (run "sudo bash" to do this but be careful), and you can unlock files in an entire volume by cd-ing to /Volumes first if need be.

chflags -R nouchg /path/to/folder

Remove OS X ACLs. To get the volume or folder down to just POSIX permissions, use chmod with the R and N switches to remove ACLs in Leopard.

chmod -RN /path/to/folder

Confirm ACLs are gone. To view ACLs in Leopard, use the ls command with el switches. If they are gone, they will not show up as shown above, and you'll just get a typical "ls -la" directory listing.

ls -el /path/to/folder

Set POSIX owner and group. Leopard's basic permissions are your administrator account that you set during the OS X install (say, "admin" for this example), and "staff" as the group. Change the owner to admin with the main group as staff.

chown -R admin:staff /path/to/folder

You can also use chgrp to change the group. Now when you do an "ls -la" on the folder, you'll see that admin and staff are set.

bash-3.2# ls -la

total 1

drwxr-xr-x@ 7 admin staff 306 Jan 1 19:17 our-2008-data

Set POSIX basic perms. You can set the umask back to default this way.

chmod -R 755 /path/to/folder

Next, let's take a look at setting ACLs.

Set ACLs on top of Basic POSIX Permissions in Leopard Server

Enable Extended Security on a Volume. Leopard has extended security on volumes set by default, but if you are working with a volume on a OS X Tiger server, you need to run fsaclctl to enable extended ACL security. Check the manual of this command to see how to disable. The command still works on Leopard, and you could use it to disable ACL permissions for whatever reason.

sudo fsaclctl -e -p /Volumes/Drive2

Then restart your server.

Set ACLs the Easy Way. If you're CLI shy, you can set ACLs in Sharing in Server Admin. Here's how:

Start Server Admin

Select the Server, and click the File Sharing tab.

Select the SharePoint, under which are the folders you want to set ACLs to, assuming the SharePoint is created.

Select the Permissions tab at the bottom, and set the ACLs with the plus and minus buttons (see the user and group list come up at the right). For POSIX drag on TOP of the existing three entries.

Click the gear button at the bottom, and choose Propagate Permissions.

Wait until it finishes.

Or you can do all of that from the command line. Use chmod to add a new ACL entry to the appropriate parent folder, while also propagating that entry to the folder's children by using the recursive (-R) flag. This command grants the "acme" group Read & Write permissions (with inheritance) to /Groups/ACME/Documents/our-2008-data :

With the above commands you should be able to straighten out any problems you might have with permissions. I hope this is helpful to someone out there. Please give me your feedback in the comments, and Enjoy!

15 comments:

Thanks so much for posting this great walkthrough! I am just starting in my adventures of administering Apple (or any other for that matter) servers, and this is a subject that has always confused me a bit. I am going to implement your suggestions this weekend. I am really hoping this helps with our permissions issues. Thanks again!

@dnm6310 - you're welcome. Apple's perms are a bit funky, but it seems every system's are just a little different while being similar. Windows, Mac, *nix, Novell Netware all have the ideas of groups and users and inheritance, but the way they work is different enough that you just have to work through it.

Have you heard of any issues with POSIX *overriding* ACL-allow, absent ACL-deny? I have a scenario where a folder has an 'owner' account with Full Control, and a 'User' account with Read-only...both entries apply to all descendants.

When the owner creates a new child folder, and sets the POSIX permissions to 'write-only' for 'everyone', the user account with the Read-only ACL is denied access. Shouldn't the user's read-only ACL override the POSIX write-only?

Hi crowe - Thanks for stopping by. I had not tried running the fsaclctl command for a while. It apparently does not exist on Snow Leopard any longer. I suppose it is Apple's way of saying "you don't need that" but I could be wrong. :-)

I have recently migrated from Leopard Server to Snow Leopard server and am having all sorts of odd problems with different network user accounts. One example is an account that cannot save changes to its dock. So every time they relog the dock is reset back to only having finder and trash icons. Other issues include extreme slowness when using Apple Mail which is cured temporarily by quitting mail and relaunching. The server does not seem busy at all during the slowdown.

I suspect the issues are all related to permissions on the user directories. Do you have any suggestions on where i might find the correct way to reset permissions on a users's home directory?

Hi Rusty - thanks for stopping by. I would say, why not do a ls -la on a working user directory, and see how it is set, then compare it to one of the ones that is not working. Maybe check the ACLs also.

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***=>> Please see my site at http://rick.cogley.info, as that is where I am blogging these days. <<=***
James Rickard Cogley (http://rick.cogley.info) is based in Tokyo Japan, and has been working in the consulting and support industry since 1990. He specializes in bilingual (Japanese - English) consulting and project management, and his company eSolia (http://www.esolia.com) is a privately-held Japanese KK focused on the same.